The present invention relates to needleless hypodermic (subcutaneous or intramuscular) injectors, i.e., devices for delivering to a body a dose of liquid medicament by way of a fine high pressure liquid stream which penetrates the skin and deposits the medicament subcutaneously or intramuscularly. More specifically, the invention concerns single-use medicine delivery units for such devices, and means for automatically disabling the units to positively prevent unsanitary and potentially infectious reuse.
For years, health workers have administered medicine to patients using syringes and needles. (It is to be understood that "medicine" and "medicament" as used herein refers generally to any type of liquid medicament or vaccine.) However, the use of syringes and needles puts health workers and patients at risk of infection through inadvertent needle-sticks or equipment misuse. In addition, syringes and needles are difficult to disinfect or sterilize, and the use of improperly sterilized syringes and needles greatly increases the risk of blood-borne disease transmission among injection recipients. Still further, syringes and needles can cause a high level of anxiety in certain patients, and reuse of dull needles can cause extreme discomfort to the injection recipient.
Disposable syringes and needles have been used to alleviate the risk of disease transmission. However, these disposable units create hazardous waste and waste disposal problems. Inadvertent painful needle sticks and consequent spread of disease and infection may result from the handling of such medical waste. In addition, particularly in some areas of the world where disposable syringes and needles often do not reach the users in adequate quantities, the disposable units may be used more than once, contrary to their intended purpose. A further drawback to disposable needles and syringes is the high costs when the units are provided for widespread use.
Several types of needleless injectors have been developed to avoid some of the drawbacks of syringes and needles. Mass-campaign jet injectors, such as the PEDO-JET, have been used to provide fast and efficient needleless injections. However, these units are very difficult to clean or sterilize upon contamination. In addition, the mass-campaign injectors utilize a complex fluid path with dead space therein, such that a substantial amount of residual medicine is retained in the fluid path. When changing from one injectant to another, the residual fluid must be cleared to prevent unacceptable mixing of medicines. This clearing process wastes a relatively large amount of medicine before the injector is ready to inject another patient.
Personal and low-workload jet injectors, such as the VITAJET and the SICIM HYPODERMIC INJECTOR JET 2000, have also been used to provide needleless injections. The SICIM low-workload injector utilizes a complex fluid path that retains residual medicine. Accordingly, the units are difficult to sterilize, and medicine is wasted through purging when changing between medicines to be administered. On the other hand, the VITAJET personal injector fills from the front through the nozzle orifice via a removable vial adaptor. This is a slow, relatively inefficient process that, in a multi-user application, could lead to cross-contamination of the reusable fluid path components.
Commonly assigned U.S. patent application Ser. No. 08/483,192, filed Jun. 7, 1995 (hereby incorporated by reference in its entirety), discloses an air-powered needleless hypodermic injector (hereinafter "APNHI") representing a significant improvement over previous designs in several respects. In particular, the injector includes a reusable (primarily stainless steel) medicine delivery unit. The delivery unit mounts in the front end of a main injector housing and is easily removed from the main injector housing for cleaning and/or sterilization, without the need for disassembly of the delivery unit.
A medicine chamber of the APNHI medicine delivery unit receives medicine from a medicine filling mechanism (including a medicine vial) through a unique side-loading fill port. A discharge piston is slidably mounted in the chamber and has a rear rod extension which engages with an air piston driven by a relatively low-pressure air source. During an injection, the air piston drives the discharge piston forward to force medicine in the chamber through an injection nozzle located at the distal end of the chamber, to form a high pressure injection stream. The design provides a simple, removable fluid path with essentially no dead space, and thereby allows medicines to be changed without purging waste. The provision of a side-loading fill port avoids cumbersome arrangements for filling the medicine delivery chamber through the front injection orifice, and the associated increased possibility of surface contamination, as exists in many other devices. In addition, since the side-loading fill port is located very close to the piston head when the piston is in its retracted position, the fill port is closed at the beginning of the piston's discharge stroke. Such positioning of the fill port eliminates the requirement (present in the rear-loading arrangements of other devices) of check-valves to prevent medicine from flowing out of the fill port during the discharge stroke. Such check valves increase costs, are very difficult to clean, and are subject to malfunction and leakage due to their repeated exposures to the extremely high injection pressures (e.g., 3000 psi) generated within the chamber.
In certain settings, such as mass immunization campaigns conducted away from health care facilities, it may be inconvenient or impractical to frequently perform cleanings and sterilization of injector components, e.g., the medicine delivery unit of the APNHI. In such settings, it would be highly desirable to be able to employ a low cost disposable medicine delivery unit that would reduce the need for equipment sterilizations. In order to prevent improper reuse of the disposable medicine delivery units, it would also be highly desirable to provide an effective low-cost disabling function.
Alchas et al. U.S. Pat. No. 5,334,144 discloses a single use disposable needleless injector. Since the entire device (including a spring mechanism and associated trigger for driving the injector piston) is disposed of after a single use, the cost per injection is relatively high.
Colavecchio U.S. Pat. No. 5,256,142 discloses a needleless injector with a "one-shot cap." In this device, a cap forming the injection orifice which is pressed against the injection recipient's skin is broken by a striker mechanism which advances with the injection piston, whereby the device cannot be reused without replacing the cap. With such a small part replaced with each injection, the costs per dose may be considerably reduced in comparison to a wholly disposable injector. However, the Colavecchio device does not guarantee that the fluid path (and therefore the next shot) will remain free from contamination.
McKinnon et al. U.S. Pat. No. 5,503,627 discloses a needless injector including an ampule which is preferably injection molded as a single part of polycarbonate. While the ampule may be provided as a pre-filled single use ampule, no mechanism is provided for positively preventing ampule reuse. Moreover, the refillable embodiments are subject to the filling and contamination difficulties described above in connection with the APNHI.